1. Field of the Invention
The present invention relates to the chlorination of phenolic compounds with gaseous chlorine, and more especially, to such chlorination of ortho-substituted phenols.
2. Description of the Prior Art
2,4,6-Trichlorophenol is an important phenolic compound which can be prepared by the chlorination of a phenolic compound substituted at the ortho positions.
The usual process for preparing 2,4,6-trichlorophenol consists of the chlorination of 2,4-dichlorophenol.
However, a small proportion of 2,4,5-trichlorophenol is concomitantly formed (on the order of 0.003 to 0.010% of the weight of 2,4,6-trichlorophenol). 2,4,6-Trichlorophenol, an intermediate for the synthesis of other valuable compounds, must not contain trace amounts of this undesirable isomer.
One solution to this problem would be to chlorinate 2,6-dichlorophenol, which would completely avoid the formation of 2,4,5-trichlorophenol. 2,3,6-Trichlorophenol, likely to be formed in this case in trace amounts, is much less troublesome than 2,4,5-trichlorophenol.
Nonetheless, when 2,6-dichlorophenol is indeed chlorinated with gaseous chlorine, it is found that adequate yields are not obtained. In particular, a large amount of 2,4,5,6,6-pentachloro-2-cyclohexenone is formed, which makes the reaction mixture very unstable and quite difficult to purity.